Vapor-compression refrigeration systems are used extensively for providing cooling in the treating, transportation, and preservation of foods and beverages and in numerous applications in a variety of chemical industries. For example, applications of these systems to petroleum refining include lubricating-oil purification, catalytic processes and condensation of volatile hydrocarbons. These systems are also prominent in other industries concerned with the separation of volatile materials by condensation. These include the production of nitrogen and oxygen from air, the manufacture of ice, and the dehydration or liquefaction of gases. Air-conditioning systems are another typical application of vapor-compression refrigeration systems.
Vapor-compression refrigeration systems typically include an evaporator wherein a refrigerant, such as ammonia, vaporizes and in the process of vaporizing provides a heat sink for absorbing heat from the matter being cooled. Vaporized refrigerant is advanced from the evaporator to a compressor and then to a condenser. In the condenser, heat is rejected from the refrigerant at a higher pressure and the refrigerant is liquefied. Liquefied refrigerant is advanced from the condenser to an expansion mechanism (e.g., expansion valve or a flash tank) and then returned to the evaporator to repeat the cycle. The degree of compression required in the compressor is dependent upon the temperature at which condensation occurs in the condenser. Typically, in most commercial and industrial refrigeration systems in use today, the heat rejection medium utilized in the condenser is cooling water which is usually maintained at temperatures in the range of about 65.degree. F. to about 85.degree. F. year-round, even though ambient air temperatures in many instances are significantly below the temperatures of such cooling waters.
Climatic weather conditions in many parts of the world, particularly the Northern Hemisphere, provide sufficiently cold temperatures at least part of the time that could be useful in supplementing the cooling capacity required of many of the above-described vapor-compression refrigeration systems. For example, in recent years, hourly temperature recordings for parts of northern Ohio indicate temperatures of 35.degree. F. or below about 36% of the time. Temperatures of 55.degree. F. or below have been similarly recorded for northern Ohio about 60% of the time. These temperatures are below the temperatures of cooling water typically used in many commercial and industrial refrigeration systems in use today and, in many instances, are below the temperatures required for the cooled materials treated by such systems.
It would be advantageous to provide a vapor-compression refrigeration system capable of utilizing the cooling capacities available from cold temperatures provided by climatic conditions during cold weather periods to supplement the cooling requirements of such systems and thereby reduce the cost and energy requirements of such systems.